Customizable stereographic projection lowres

This is basically the same as http://www.thingiverse.com/thing:295281 but with just 75x75 pixels instead of 150x150, this works in customizer just fine, maybe the highres version will work later, I filed a bug report for customizer. If you need higher resolution you can still do it on your local machine with OpenSCAD.
[Edit] Minor bug with the outer borders fixed.